THE SIMPLEST HOMEMADE ELECTRICAL GENERATOR

MAKING THE GENERATOR
Although you can simply wind the coil directly around the plastic film can (see picture of the first prototype) it is neater and easier to make a simple bobin to wind the coil round. Here’s how to do it:

Step 1
Find a 35mm plastic film can and remove the lid. Cut out two cardboard circles about 50mm diameter and cut out their centres (33mm diameter hole) so that they fit snugly onto the canister. Space the two circles about 1cm either side of the center of the can. Wind on a few turns of insulation tape on to the can, either side of the cardboard to hold them in place.

Step 2
Use the cardboard circles as a bobbin (or former) on which to wind the coil. Wind on 500 to 1000 turns of thin, insulated copper wire. Add a layer of sellotape to keep them from un-winding. Remember to leave about 10cm or so of wire free at each end.

Step 3
Scrape off some of the insulation (say 5mm or so) from the ends of the wire (using sandpaper) and connect to the LED (it does not matter which way round). Solder the connections if possible. Use some sellotape to secure the wire and LED to the bottom of the can.

Step 4
Pop a small (but powerful) magnet into the can and snap the lid back on. Hold the can between thumb and forefinger at the two ends of the can (with thumb or forefinger on the lid to stop it coming off !) and shake. The LED will light

HOW THE GENERATOR WORKS

A generator works by a magnetic field inducing a voltage into a coil of wire. Important points to note are that the voltage increases as the number of turns of wire on the coil becomes larger and the size of the coil and the strength of the magnetic field increase. The magnetic field (or the coil) needs to be in constant motion to produce/induce the electricity into the coil. This can be done by moving the magnet or by moving the coil - the effect is the same. The coil (or the magnet) needs to move in such a way that the coil continually passes through the magnetic field.

The type of wire in the coil is also important. For example, thick wire means there will be less power loss, but the down side is that the coil will get very large when a great number of turns is needed. In a practical generator some trade off has therefore to be found between the size of magnet, coil and the wire.

The peak voltage generated by this little device is given by:

V = A x M x N

Where A is the cross sectional area of the can (0.0008 m²), M is the rate of change of magnetic field (ca. we need to use very strong magnets having a surface field of say 1 Tesla (see magnet info. below), so shaking it say 5 times a sec we get M = 5 Tesla / sec) and N the number of turns.
If we want an LED to light brightly we need to generate peak voltages of about 4V;

rearanging the formula allows us to estimate the number of turns:

N = V / (A x M) = 4 / (0.0008 x 5) = about 1000 turns - happy winding !

AC or DC
This simple generator is called an AC generator. This means that the voltage appearing at the two wires alternates between + and -, and - and + each time the magnet goes from one end of the can to the other. As a result the generator can light a bulb or an LED without you having to worry about which way round the connections need to go (as they are effectively reversing all the time anyway). However, this simple generator is not good for running radios, calculators or other devices that need a direct current (DC) that is produced for example from a battery.

source:  www.creative-science.org.uk

Tags: bobin, magnet, magnetic field